1. Technical Field
The invention relates generally to semiconductor device fabrication, and more particularly, to a method for forming a mask for implanting a substrate, where the mask includes an implant stopping layer, and a mask so formed.
2. Background Art
In the semiconductor fabrication industry continual miniaturization of structures presents challenges relative to modifying current techniques. One challenge is addressing problems related to photolithography. Photolithography is a process used in the semiconductor fabrication industry in which a photo-sensitive material, i.e., a photoresist, is laid upon a substrate, imaged and then etched to leave a pattern that can be used to generate other structures within the substrate. As miniaturization continues, the dimensions of patterned photoresists are also being minimized. Some processing, for example, deep well ion implants, require very thick layers of photoresist to block ion implantation into areas under the photoresist in which the implantation is not desired. These patterned single layer photoresists have a relatively high aspect ratio, i.e., patterned photoresist height to patterned line width, and, as a result, are subject to collapse. For example, FIG. 1 shows a conventional patterned photoresist 10 over a substrate 12 having trench isolations 14 therein. Patterned photoresist 10 has a relatively high aspect ratio. As shown in FIG. 2, patterned photoresist 10 is subject to capillary-induced line collapses in which capillary action within patterned openings 16 (FIG. 1) draws the photoresist inwardly and causes a collapse.
One approach to address this situation has been to employ hard masks having two layers, one layer including silicon oxide and/or silicon nitride to block the ion implantation. While bilayer photoresist masks have lower aspect ratios compared to single layer masks, during removal of these bilayer masks, trench isolations 14 (FIG. 2) within substrate 12, which typically include silicon oxide and/or silicon nitride based materials, can be degraded because the etching chemistry used to remove the hard mask is also effective on the trench isolation. In addition, these conventional bilayer photoresist masks must be inorganic, which prevents use of a wide variety of organic photoresists. In addition, the total density of the photoresist mask leads to ion scattering, which causes proximity effects in neighboring devices.
In view of the foregoing, there is a need in the art for a solution to the problems of the related art.